Investigations in our laboratory will continue to be directed toward development of knowledge of blood platelet function in normal hemostasis, their role in the pathogenesis of inherited and acquired bleeding disorders, and their contribution to protection and injury of blood vessels, thrombosis and arteriosclerosis. Analytical, scanning and transmission electron microscopy, freeze-fracture, cytochemistry, immunofluorescence and immunoelectron microscopy, together with cyclic nucleotide, adenine nucleotide and eicosanoid biochemistry and advanced physiological techniques, including measurements of calcium levels and flux with Quin 2 and Fura 2, micropipette elastimetry, the Baumgartner technique and lumiaggregometry will be used to develop new information on these problems and related areas. Emphasis has been placed on six specific aims. Specific aim 1 will elucidate the role of membranes and membrane systems in platelet stimulus activation coupling with particular attention to calcium regulation. Approaches to the cytoskeleton in specific aim 2 will reveal its role in platelet resistance to deformation, the asociations between circumferential microtubule coils resulting in support of discoid shape and the interactions between actin microfilaments, microtubules and the cell membrane. Specific aim 3 will resolve current controversies regarding mechanisms of platelet secretion. A new model of platelet stimulus-activation-contraction-secretion coupling has resulted from our preliminary studies and will serve as the basis for new investigations on the subject in specific aim 4. The relationship between platelet deformability and platelet-vessel wall interaction will be explored in specific aim 5 and may serve as a new basis for selecting anti-platelet drugs and following patients with hyperlipidemia. The 6th specific aim will continue studies on established platelet disorders and explore three new conditions in which abnormal structure may be related to defects in regulation of calcium flux. Accomplishment of these aims in the next five years will bring us very close to achieving the overall goals guiding this project.